Fuel cell pump and method for controlling fuel cell pump

ABSTRACT

A pump for a fuel cell includes a pump portion, a motor, a controller, a housing, and a temperature detector. The controller executes an activation control and a sensorless vector control. In the activation control, the controller executes a cold activation mode process when the outside air temperature is less than or equal to a set temperature. In the cold activation mode process, the controller executes at least one of increasing a value of an activation current supplied to the motor relative to when a normal activation mode process is executed or setting a supply duration of the activation current to the motor to be longer than that of when the normal activation mode process is executed.

BACKGROUND 1. Field

The following description relates to a pump for a fuel cell and a methodfor controlling a pump for a fuel cell.

2. Description of Related Art

Vehicles having a fuel cell system have recently been in practical use.The fuel cell system includes a fuel cell that generates power byproducing a chemical reaction of hydrogen as a fuel gas with oxygen asan oxidant gas that is contained in the air. A pump for a fuel cell isused, for example, as a pump that supplies hydrogen to the fuel cell.Japanese Laid-Open Patent Publication No. 2006-283664 discloses a Rootspump, which is an example of a fuel cell pump. The Roots pump includes ahousing, a pump portion that supplies hydrogen to the fuel cell, a pumpchamber defined in the housing and accommodating the pump portion, and amotor that drives the pump portion. The Roots pump further includes acontroller that controls the driving of the motor. When activating thepump portion, the controller supplies an activation current having apredetermined value to the motor to control the driving of the motor.

In the fuel cell pump, hydrogen that has not reacted with oxygen in thefuel cell (hydrogen off-gas) is drawn into the pump chamber. Whenhydrogen is drawn into the pump chamber, the pump chamber also draws inwater that has been produced as the fuel cell generates power. Thus, forexample, when the operation of the pump portion is stopped in a coldenvironment, the water freezes into ice in the pump chamber. If waterfreezes into ice between the pump portion and an inner wall of thehousing defining the pump chamber, the pump portion may adhere to thehousing via the ice.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

It is an objective of the present disclosure to provide an improved pumpfor a fuel cell and an improved method for controlling a pump for a fuelcell.

To achieve the above objective, a first aspect is a pump for a fuelcell. The pump includes a pump portion configured to supply a fuel gasor an oxidant gas to the fuel cell, a motor configured to drive the pumpportion, a controller configured to control driving of the motor, ahousing including a pump chamber accommodating the pump portion, a motorchamber accommodating the motor, and a control chamber accommodating thecontroller, a temperature detector configured to detect an outside airtemperature. The controller is configured to execute an activationcontrol that is executed until the pump portion is activated, and asensorless vector control that is executed after the pump portion isactivated. In the activation control, the controller is configured toexecute a normal activation mode process when the outside airtemperature detected by the temperature detector is greater than apredetermined set temperature, and execute a cold activation modeprocess when the outside air temperature detected by the temperaturedetector is less than or equal to the set temperature. In the coldactivation mode process, the controller is configured to execute atleast one of increasing a value of an activation current supplied to themotor relative to when the normal activation mode process is executed orsetting a supply duration of the activation current to the motor to belonger than that of when the normal activation mode process is executed.The controller is configured to shift from the activation control to thesensorless vector control after the pump portion is activated.

To achieve the above objective, a second aspect is a method forcontrolling a pump for a fuel cell. The pump includes a pump portionconfigured to supply a fuel gas or an oxidant gas to the fuel cell, amotor configured to drive the pump portion, and a controller configuredto control driving of the motor. The method includes an activationcontrol that is executed until the pump portion is activated, and asensorless vector control that is shifted from the activation controland executed after the pump portion is activated. The activation controlincludes comparing a predetermined set temperature with an outside airtemperature detected by a temperature detector, which detects theoutside air temperature, based on a result of the comparison, executinga normal activation mode process when the outside air temperaturedetected by the temperature detector is greater than the predeterminedset temperature, and executing a cold activation mode process when theoutside air temperature detected by the temperature detector is lessthan or equal to the set temperature. The cold activation mode processincludes executing at least one of increasing a value of an activationcurrent supplied to the motor relative to when the normal activationmode process is executed or setting a supply duration of the activationcurrent to the motor to be longer than that of when the normalactivation mode process is executed.

Other aspects and advantages of the present disclosure will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional plan view showing an embodiment of a fuelcell pump.

FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1 .

FIG. 3 is a graph showing the relationship between current and time whena cold activation mode process is executed to activate a pump portion.

FIG. 4 is a flowchart illustrating the controlling of an inverter.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

This description provides a comprehensive understanding of the methods,apparatuses, and/or systems described. Modifications and equivalents ofthe methods, apparatuses, and/or systems described are apparent to oneof ordinary skill in the art. Sequences of operations are exemplary, andmay be changed as apparent to one of ordinary skill in the art, with theexception of operations necessarily occurring in a certain order.Descriptions of functions and constructions that are well known to oneof ordinary skill in the art may be omitted.

Exemplary embodiments may have different forms, and are not limited tothe examples described. However, the examples described are thorough andcomplete, and convey the full scope of the disclosure to one of ordinaryskill in the art.

Embodiments of a fuel cell pump and a method for controlling a fuel cellpump will now be described with reference to FIGS. 1 to 4 . The fuelcell pump of the present embodiment is used as a pump configured tosupply hydrogen to a fuel cell that generates power by producing achemical reaction of hydrogen as a fuel gas with oxygen as an oxidantgas contained in the air.

As shown in FIG. 1 , a housing 11 of a fuel cell pump 10 is tubular andincludes a motor housing 12, a gear housing 13, a rotor housing 14, anda cover member 15. The motor housing 12 includes a flat end wall 12 aand a tubular peripheral wall 12 b extending from a peripheral portionof the end wall 12 a. Thus, the motor housing 12 has the shape of a tubehaving a closed end. The gear housing 13 includes a flat end wall 13 aand a tubular peripheral wall 13 b extending from a peripheral portionof the end wall 13 a. Thus, the gear housing 13 has the shape of a tubehaving a closed end. The gear housing 13 is coupled to an open end ofthe peripheral wall 12 b of the motor housing 12. The end wall 13 a ofthe gear housing 13 closes the opening of the peripheral wall 12 b ofthe motor housing 12.

The rotor housing 14 includes a flat end wall 14 a and a tubularperipheral wall 14 b extending from a peripheral portion of the end wall14 a. Thus, the rotor housing 14 has the shape of a tube having a closedend. The rotor housing 14 is coupled to an open end of the peripheralwall 13 b of the gear housing 13. The end wall 14 a of the rotor housing14 closes the opening of the peripheral wall 13 b of the gear housing13. The cover member 15 is flat. The cover member 15 is coupled to anopen end of the peripheral wall 14 b of the rotor housing 14 and isopposed to the end wall 14 a to close the peripheral wall 14 b. Theaxial direction of the peripheral wall 12 b of the motor housing 12, theaxial direction of the peripheral wall 13 b of the gear housing 13, andthe axial direction of the peripheral wall 14 b of the rotor housing 14conform to each other.

The fuel cell pump 10 includes a driving shaft 16 and a driven shaft 17that are disposed parallel to each other and rotationally supported bythe housing 11. The rotational axial direction of each of the drivingshaft 16 and the driven shaft 17 conforms to the axial direction of eachof the peripheral walls 12 b, 13 b, and 14 b. A disc-shaped driving gear18 is fixed to the driving shaft 16. A disc-shaped driven gear 19 isfixed to the driven shaft 17 and meshes with the driving gear 18. Adriving rotor 20 is arranged on the driving shaft 16. A driven rotor 21is arranged on the driven shaft 17 to mesh with the driving rotor 20.

The fuel cell pump 10 includes a motor 22 that rotates the driving shaft16 to drive the driving rotor 20 and the driven rotor 21. The motor 22is accommodated in a motor chamber 23 arranged in the housing 11. Themotor chamber 23 is defined by the end wall 12 a of the motor housing12, the peripheral wall 12 b of the motor housing 12, and the end wall13 a of the gear housing 13. The motor 22 includes a tubular motor rotor22 a and a tubular stator 22 b. The motor rotor 22 a is fixed to thedriving shaft 16 to rotate integrally with the driving shaft 16. Thestator 22 b is fixed to an inner surface of the peripheral wall 12 b ofthe motor housing 12 and extends around the motor rotor 22 a. The stator22 b includes a coil 22 c wound around teeth, which are not illustrated.When power is supplied to the coil 22 c, the motor 22 is driven torotate the motor rotor 22 a integrally with the driving shaft 16.

A gear chamber 24 is arranged in the housing 11 to accommodate thedriving gear 18 and the driven gear 19. The gear chamber 24 is definedby the end wall 13 a of the gear housing 13, the peripheral wall 13 b ofthe gear housing 13, and the end wall 14 a of the rotor housing 14. Thedriving gear 18 and the driven gear 19 mesh with each other and areaccommodated in the gear chamber 24. The gear chamber 24 encapsulatesoil. The oil lubricates the driving gear 18 and the driven gear 19 andlimits increases in the temperature of the driving gear 18 and thedriven gear 19. The driving gear 18 and the driven gear 19, which areimmersed in the oil, can rotate at a relatively high speed withoutresulting in galling and wear.

The housing 11 includes a rotor chamber 25, which corresponds to a pumpchamber accommodating the driving rotor 20 and the driven rotor 21. Therotor chamber 25 is defined by the end wall 14 a of the rotor housing14, the peripheral wall 14 b of the rotor housing 14, and the covermember 15. The driving rotor 20 and the driven rotor 21 mesh with eachother and are accommodated in the rotor chamber 25.

The fuel cell pump 10 includes an inverter 60, which corresponds to acontroller configured to control the driving of the motor 22. A tubularcover 61 having a closed end is attached to the end wall 12 a of themotor housing 12. The end wall 12 a of the motor housing 12 and thecover 61 define an inverter chamber 62, which corresponds to a controlchamber accommodating the inverter 60. In the present embodiment, therotor chamber 25, the gear chamber 24, the motor chamber 23, and theinverter chamber 62 are arranged in this order in the rotational axialdirection of the driving shaft 16.

The end wall 13 a of the gear housing 13 separates the gear chamber 24and the motor chamber 23 in the rotational axial direction of thedriving shaft 16. The end wall 14 a of the rotor housing 14 separatesthe gear chamber 24 and the rotor chamber 25 in the rotational axialdirection of the driving shaft 16. The driving shaft 16 extends throughthe end wall 13 a of the gear housing 13 and the end wall 14 a of therotor housing 14. The driven shaft 17 extends through the end wall 14 aof the rotor housing 14.

The end wall 13 a of the gear housing 13 has an inner surface 13 eincluding a first bearing accommodation recess 27. The first bearingaccommodation recess 27 has the shape of a circular hole to accommodatea first bearing 26 that rotationally supports the driving shaft 16. Thedriving shaft 16 extends through the first bearing accommodation recess27. The first bearing accommodation recess 27 has a bottom surface 27 aincluding a first seal accommodation recess 29, through which thedriving shaft 16 extends. The first seal accommodation recess 29 has theshape of a circular hole to accommodate an annular first seal member 28that seals the space between the gear chamber 24 and the motor chamber23. The first seal accommodation recess 29 is in communication with thefirst bearing accommodation recess 27. In addition, an annular firstspacer 30 is arranged between the first bearing 26 and the bottomsurface 27 a of the first bearing accommodation recess 27 in therotational axial direction of the driving shaft 16.

The end wall 14 a of the rotor housing 14 has an outer surface 14 eincluding a second bearing accommodation recess 32 and a third bearingaccommodation recess 37. The second bearing accommodation recess 32 andthe third bearing accommodation recess 37 have the shape of a circularhole to accommodate a second bearing 31 and a third bearing 36, whichrotationally support the driving shaft 16 and the driven shaft 17,respectively. The driving shaft 16 extends through the second bearingaccommodation recess 32. The driven shaft 17 extends through the thirdbearing accommodation recess 37.

The second bearing accommodation recess 32 has a bottom surface 32 aincluding a second seal accommodation recess 34, through which thedriving shaft 16 extends. The second seal accommodation recess 34 hasthe shape of a circular hole to accommodate an annular second sealmember 33 that seals the space between the gear chamber 24 and the rotorchamber 25. The second seal accommodation recess 34 is in communicationwith the second bearing accommodation recess 32. In addition, an annularsecond spacer 35 is arranged between the second bearing 31 and thebottom surface 32 a of the second bearing accommodation recess 32 in therotational axial direction of the driving shaft 16.

The third bearing accommodation recess 37 has a bottom surface 37 aincluding a third seal accommodation recess 39, through which the drivenshaft 17 extends. The third seal accommodation recess 39 has the shapeof a circular hole to accommodate an annular third seal member 38 thatseals the space between the gear chamber 24 and the rotor chamber 25.The third seal accommodation recess 39 is in communication with thethird bearing accommodation recess 37. In addition, an annular thirdspacer 40 is arranged between the third bearing 36 and the bottomsurface 37 a of the third bearing accommodation recess 37 in therotational axial direction of the driven shaft 17.

The inner surface 13 e of the end wall 13 a of the gear housing 13includes a fourth bearing accommodation recess 42 having the shape of acircular hole to accommodate a fourth bearing 41. The fourth bearing 41rotationally supports an end, that is, a first end, of the driven shaft17. The fourth bearing accommodation recess 42 has an open edge that iscontinuous with the inner surface 13 e of the end wall 13 a of the gearhousing 13. The first end of the driven shaft 17 is disposed in thefourth bearing accommodation recess 42 and rotationally supported by thefourth bearing 41. The other end, that is, a second end, of the drivenshaft 17 extends through the third bearing accommodation recess 37 andthe third seal accommodation recess 39 and projects to the rotor chamber25. The driven rotor 21 is coupled to the second end of the driven shaft17. The second end of the driven shaft 17 is a free end. Thus, thedriven shaft 17 is supported by the housing 11 in a cantilevered manner.

The end wall 12 a of the motor housing 12 has an inner surface 12 eincluding a tubular bearing portion 44. The bearing portion 44accommodates a fifth bearing 43 rotationally supporting an end, that is,a first end, of the driving shaft 16. The first end of the driving shaft16 is disposed in the bearing portion 44 and rotationally supported bythe fifth bearing 43. The other end, that is, a second end, of thedriving shaft 16 extends through the first seal accommodation recess 29,the first bearing accommodation recess 27, the gear chamber 24, thesecond bearing accommodation recess 32, and the second sealaccommodation recess 34 and projects to the rotor chamber 25. Thedriving rotor 20 is coupled to the second end of the driving shaft 16.The second end of the driving shaft 16 is a free end. Thus, the drivingshaft 16 is supported by the housing 11 in a cantilevered manner.

As shown in FIG. 2 , each of the driving rotor 20 and the driven rotor21 is shaped as a numeral 8 (hourglass-shaped) in a cross-sectional viewthat is orthogonal to the rotational axial directions of the drivingshaft 16 and the driven shaft 17. The driving rotor 20 includes twolobes 20 a and recesses 20 b located between the two lobes 20 a. Thedriven rotor 21 includes two lobes 21 a and recesses 21 b locatedbetween the two lobes 21 a.

The driving rotor 20 and the driven rotor 21 are rotatable in the rotorchamber 25 while repeating engagement of the lobes 20 a of the drivingrotor 20 with the recesses 21 b of the driven rotor 21 and engagement ofthe recesses 20 b of the driving rotor 20 with the lobes 21 a of thedriven rotor 21. The driving rotor 20 rotates in arrow R1 directionshown in FIG. 2 . The driven rotor 21 rotates in arrow R2 directionshown in FIG. 2 .

The peripheral wall 14 b of the rotor housing 14 includes an intake port45 in a lower portion in a gravitational direction Z1. The peripheralwall 14 b of the rotor housing 14 also includes a discharge port 46 inan upper portion in the gravitational direction Z1. The intake port 45is connected to a hydrogen outlet 50 b of a fuel cell 50 by a firstconnection pipe 50 a. The discharge port 46 is connected to a hydrogeninlet 50 d of the fuel cell 50 by a second connection pipe 50 c.

As shown in FIGS. 1 and 2 , when the motor 22 is driven to rotate thedriving shaft 16, the driven shaft 17 rotates in the opposite directionfrom the driving shaft 16 via the gear coupling of the driving gear 18and the driven gear 19 that are meshed with each other. Thus, thedriving rotor 20 and the driven rotor 21, which are engaged with eachother, rotate in opposite directions. In the fuel cell pump 10, when thedriving rotor 20 and the driven rotor 21 rotate, hydrogen that has notreacted with oxygen in the fuel cell 50 (hydrogen off-gas) is drawn intothe rotor chamber 25 through the hydrogen outlet 50 b, the firstconnection pipe 50 a, and the intake port 45. The hydrogen drawn intothe rotor chamber 25 is discharged from the discharge port 46 and issupplied to the fuel cell 50 through the second connection pipe 50 c andthe hydrogen inlet 50 d in accordance with the rotation of the drivingrotor 20 and the driven rotor 21. Thus, the driving rotor 20 and thedriven rotor 21 are configured to be a pump portion P configured tosupply hydrogen to the fuel cell 50. The fuel cell pump 10 of thepresent embodiment is a Roots pump in which the pump portion P includesthe driving rotor 20 and the driven rotor 21.

As shown in FIG. 1 , the fuel cell pump 10 includes a temperature sensor63, which corresponds to a temperature detector configured to detect anoutside air temperature T1, and a pressure sensor 64 configured todetect a discharge pressure of the fuel cell pump 10. The pressuresensor 64 detects the pressure of hydrogen discharged from the rotorchamber 25 through the discharge port 46 to the second connection pipe50 c by the rotation of the driving rotor 20 and the driven rotor 21.The temperature sensor 63 and the pressure sensor 64 are electricallyconnected to the inverter 60.

The inverter 60 stores, in advance, a determination program thatdetermines that the pump portion P is activated upon reception of adischarge pressure detection signal from the pressure sensor 64, anddetermines that the pump portion P is stopped when the dischargepressure detection signal is not received from the pressure sensor 64.The state in which “the pump portion P is stopped” refers to a state inwhich the driving rotor 20 and the driven rotor 21 are not rotating. Thestate in which “the pump portion P has started to be activated” refersto a state in which the driving rotor 20 and the driven rotor 21 havestarted to rotate. The inverter 60 is configured to execute anactivation control, which is executed until the pump portion P isactivated, and a sensorless vector control, which is executed after thepump portion P is activated.

The inverter 60 receives a signal related to the outside air temperatureT1, which is detected by the temperature sensor 63. The inverter 60stores, in advance, a temperature comparison program that compares theoutside air temperature T1 detected by the temperature sensor 63 with apredetermined set temperature T2 based on the signal received from thetemperature sensor 63. The inverter 60 stores, in advance, a programthat executes a normal activation mode process when the outside airtemperature T1 detected by the temperature sensor 63 is greater than thepredetermined set temperature T2, and executes a cold activation modeprocess when the outside air temperature T1 detected by the temperaturesensor 63 is less than or equal to the set temperature T2.

When the outside air temperature T1 detected by the temperature sensor63 is greater than the set temperature T2, it is assumed that water willnot freeze in the rotor chamber 25 even if present in the rotor chamber25. When the outside air temperature T1 detected by the temperaturesensor 63 is less than or equal to the set temperature T2, it is assumedthat water is frozen in the rotor chamber 25 if present in the rotorchamber 25. Such assumptions are obtained in advance by tests or thelike. Thus, the set temperature T2 is a temperature that is obtained inadvance by tests or the like for determining whether water is frozen inthe rotor chamber 25 when present in the rotor chamber 25.

The inverter 60 stores, in advance, a program that supplies anactivation current, which is the minimum value of the activation currentto activate the pump portion P, to the motor 22 for the minimum amountof time when the normal activation mode process is executed. The periodof the activation current during the normal activation mode process isinvariably set to be fixed.

The inverter 60 stores, in advance, a program that increases the valueof the activation current supplied to the motor 22 when the coldactivation mode process is executed relative to when the normalactivation mode process is executed, and also sets a supply duration ofthe activation current to the motor 22 to be longer when the coldactivation mode process is executed than when the normal activation modeprocess is executed. The inverter 60 executes this program to performthe activation control on the pump portion P. More specifically, forexample, when the cold activation mode process is executed, the inverter60 supplies the motor 22 with the activation current having a value thatis approximately twice the value of the activation current that issupplied to the motor 22 when the normal activation mode process isexecuted. In addition, for example, when the cold activation modeprocess is executed, the inverter 60 sets the supply duration of theactivation current to the motor 22 to be ten times longer than thesupply duration of the activation current to the motor 22 when thenormal activation mode process is executed.

As shown in FIG. 3 , the inverter 60 stores, in advance, a program thatexecutes the cold activation mode process multiple times. For example,when the cold activation mode process is executed for the first time andthe discharge pressure detection signal is not received from thepressure sensor 64, the inverter 60 determines that the pump portion Pis stopped, that is, the pump portion P has not been activated, andexecutes the cold activation mode process again.

The inverter 60 stores, in advance, a program that gradually shortensthe period of the activation current during the cold activation modeprocess. The period of the activation current is set so as to graduallyshorten during the cold activation mode process.

The inverter 60 stores, in advance, a program that executes a vectorcontrol mode process, which performs a sensorless vector control on themotor 22, when the discharge pressure detection signal is received fromthe pressure sensor 64 and it is determined that the pump portion P hasstarted to be activated. The inverter 60 executes this program toperform the sensorless vector control on the motor 22.

In addition, the inverter 60 stores, in advance, a program that executesan abnormality determination process that determines an abnormality hasoccurred when the discharge pressure detection signal is not receivedfrom the pressure sensor 64 after the normal activation mode process isexecuted.

The operation of the present embodiment will now be described along thedescription of a method for controlling the fuel cell pump 10 in thepresent embodiment. The inverter 60 executes the activation control,which is executed until the pump portion P is activated, and thesensorless vector control, which is shifted from the activation controland executed after the pump portion P is activated.

As shown in FIG. 4 , to activate the pump portion P, in step S11, theinverter 60 receives a signal related to the outside air temperature T1detected by the temperature sensor 63. In step S12, the inverter 60executes a temperature comparison step that compares the outside airtemperature T1 detected by the temperature sensor 63 with thepredetermined set temperature T2 based on the signal received from thetemperature sensor 63.

If the comparison result of the temperature comparison step executed instep S12 shows that the outside air temperature T1 detected by thetemperature sensor 63 is greater than the set temperature, the inverter60 proceeds to step S13 and executes a process execution step thatexecutes the normal activation mode process in step S13. Thus, theinverter 60 supplies the activation current, which is the minimum valueof the activation current to activate the pump portion P, to the motor22 for the minimum amount of time. At this time, the period of theactivation current is invariably fixed. In step S14, the inverter 60determines whether the discharge pressure detection signal is receivedfrom the pressure sensor 64. If it is determined in step S14 that thedischarge pressure detection signal has been received from the pressuresensor 64, the inverter 60 proceeds to the normal control in step S15.The inverter 60 determines that the pump portion P has started to beactivated and executes, in step S15, a vector control mode process thatperforms sensorless vector control on the motor 22. If it is determinedin step S14 that the discharge pressure detection signal has not beenreceived from the pressure sensor 64, the inverter 60 proceeds to stepS16 and executes the abnormality determination process based ondetermination that an abnormality has been detected.

In the fuel cell pump 10, hydrogen that has not reacted with oxygen inthe fuel cell 50 (hydrogen off-gas) is drawn into the rotor chamber 25.Water that has been produced as a result of power generation of the fuelcell 50 generates power is also drawn into the rotor chamber 25. Thus,for example, when the operation of the pump portion P is stopped in acold environment, the water freezes into ice in the rotor chamber 25. Inthe rotor chamber 25, if water is frozen into ice between the innersurface of the motor housing 12 defining the rotor chamber 25 and thedriving rotor 20 and the driven rotor 21, the driving rotor 20 and thedriven rotor 21 may be adhered to the rotor housing 14 by the ice.

If the comparison result of the temperature comparison step executed instep S12 shows that the outside air temperature T1 detected by thetemperature sensor 63 is less than or equal to the set temperature T2,the inverter 60 proceeds to step S17. In step S17, the inverter 60executes a process execution step that executes the cold activation modeprocess. As a result, the value of the activation current supplied tothe motor 22 is increased relative to when the normal activation modeprocess is executed. Also, the supply duration of the activation currentto the motor 22 is increased relative to when the normal activation modeprocess is executed. That is, the maximum value of the activationcurrent in the cold activation mode process is greater than the maximumvalue of the activation current in the normal activation mode process.

In addition, in this case, the inverter 60 gradually shortens the periodof the activation current, which is different from the period of theactivation current when the normal activation mode process is executed.For example, as the outside air temperature T1 detected by thetemperature sensor 63 becomes lower than the set temperature T2, it islikely that the driving rotor 20 and the driven rotor 21 are morestrongly adhered to the rotor housing 14. In such a case, when the motor22 starts to rotate at a low speed, the driving rotor 20 and the drivenrotor 21 are separated from the ice present between the inner wall ofthe rotor housing 14 and the driving rotor 20 and the driven rotor 21more readily than when the motor 22 quickly starts to rotate at a highspeed.

In step S17, when the cold activation mode process is executed for thefirst time, the inverter 60 proceeds to step S18 and determines in stepS18 whether the discharge pressure detection signal has been receivedfrom the pressure sensor 64. In step S18, if it is determined that thedischarge pressure detection signal has not been received from thepressure sensor 64, the inverter 60 proceeds to step S17 and executesthe cold activation mode process for the second time. Thus, when thecold activation mode process is executed for the first time and thedischarge pressure detection signal has not been received from thepressure sensor 64, the inverter 60 determines that the pump portion Pis stopped, that is, the pump portion P has not been activated, andagain executes the cold activation mode process.

When the inverter 60 executes the cold activation mode process for thesecond time, the switching of the rotation direction of the motor 22generates impact force, which is transferred to the ice present betweenthe inner surface of the motor housing 12 defining the rotor chamber 25and the driving rotor 20 and the driven rotor 21. As a result, thedriving rotor 20 and the driven rotor 21 are separated from the icepresent between the inner surface of the motor housing 12 and thedriving rotor 20 and the driven rotor 21, and the driving rotor 20 andthe driven rotor 21 start to rotate. If it is determined in step S18that the discharge pressure detection signal has been received from thepressure sensor 64, the inverter 60 proceeds to the normal control instep S15. The inverter 60 determines that the pump portion P has startedto be activated and executes, in step S15, the vector control modeprocess that performs sensorless vector control on the motor 22.

In the present embodiment, the pump portion P is activated when the coldactivation mode process is executed twice. If the pump portion P is notactivated when the cold activation mode process is executed twice, theinverter 60 repeatedly executes the process from step S17.

Thus, the activation control includes steps S11, S12, S13, S14, S17, andS18. The sensorless vector control includes step S15.

To facilitate the understanding of the effects of the presentembodiment, the conventional fuel cell pump described in the Backgroundsection will be referred to.

As described in the Background section, the pump portion may be adheredto the housing by ice in a cold environment. The controller may beconfigured to invariably supply a predetermined value of the activationcurrent to the motor to activate the pump portion without taking intoconsideration whether the pump portion is adhered to the housing by ice.In this configuration, for example, when the pump portion is adhered tothe housing by ice, it takes a longer time to activate the pump portionthan when the pump portion is not adhered to the housing by ice. Thislowers responsiveness.

In this respect, the controller may be configured to invariably supplythe motor, to activate the pump portion, with the activation currenthaving a value such that the pump portion is immediately drivable evenwhen the pump portion is adhered to the housing by ice. In thisconfiguration, for example, even when the pump portion is not adhered tothe housing by ice, the controller supplies the motor with theactivation current having a value such that the pump portion that isadhered to the housing by ice is drivable. Thus, the activation currenthas an overly large value and is supplied to the motor. This results inunnecessary power consumption.

The present embodiment has the following advantages.

(1) When the outside air temperature T1 detected by the temperaturesensor 63 is less than or equal to the set temperature T2, the inverter60 executes the cold activation mode process. That is, for example, evenwhen the driving rotor 20 and the driven rotor 21 are adhered to therotor housing 14 by ice, the following two actions are both executed toactivate the pump portion P. The two actions are increasing the value ofthe activation current supplied to the motor 22 relative to when thenormal activation mode process is executed and setting the supplyduration of the activation current to the motor 22 to be longer thanthat of when the normal activation mode process is executed. This avoidsa situation in which, for example, the inverter 60 executes the normalactivation mode process to activate the pump portion P regardless of thedriving rotor 20 and the driven rotor 21 being adhered to the rotorhousing 14 by ice. As a result, the time for activating the pump portionis shortened.

When the outside air temperature T1 detected by the temperature sensor63 is greater than the predetermined set temperature T2, the inverter 60executes the normal activation mode process. This avoids a situation inwhich, for example, at least one of increasing the value of theactivation current supplied to the motor 22 relative to when the normalactivation mode process is executed or setting the supply duration ofthe activation current to the motor 22 to be longer than that of whenthe normal activation mode process is executed, as in the coldactivation mode process, is executed to activate the pump portion Pregardless of the driving rotor 20 and the driven rotor 21 not beingadhered to the rotor housing 14 by ice. As a result, the supply of theactivation current having an excessive value to the motor 22 and anunnecessary extension of the supply duration of the activation currentto the motor 22 are avoided. This reduces unnecessary power consumption.As described above, while shortening the time for activating the pumpportion P, unnecessary power consumption is reduced.

(2) The pump portion P is activated further readily as compared to, forexample, a configuration that executes only one of increasing the valueof the activation current to the motor 22 or setting the supply durationof the activation current to the motor 22 to be longer than that of whenthe normal activation mode process is executed.

(3) For example, when the inverter 60 executes the cold activation modeprocess for the first time and the pump portion P is not activated, theinverter 60 again executes the cold activation mode process. In thiscase, impact force is generated by the switching of the rotationdirection of the motor 22 is transmitted to the ice present between theinner surface of the rotor housing 14 defining the rotor chamber 25 andthe driving rotor 20 and the driven rotor 21. This facilitates theseparation of the driving rotor 20 and the driven rotor 21 from the icepresent between the inner surface of the rotor housing 14 and thedriving rotor 20 and the driven rotor 21, thereby allowing the pumpportion P to be readily activated.

(4) For example, as the outside air temperature T1 detected by thetemperature sensor 63 becomes lower than the set temperature T2, it islikely that the driving rotor 20 and the driven rotor 21 are morestrongly adhered to the rotor housing 14. In such a case, when the motor22 starts to rotate at a low speed, the driving rotor 20 and the drivenrotor 21 are separated from the ice present between the inner wall ofthe rotor housing 14 and the driving rotor 20 and the driven rotor 21more readily than when the motor 22 quickly starts to rotate at a highspeed. The inverter 60 gradually shortens the period of the activationcurrent during the cold activation mode process. In this configuration,the motor 22 starts to rotate at a lower speed than in a configurationin which the period of activation current is invariably fixed. Thisallows for the separation of the driving rotor 20 and the driven rotor21 from ice present between the inner surface of the rotor housing 14and the driving rotor 20 and the driven rotor 21 even when the drivingrotor 20 and the driven rotor 21 are strongly adhered to the rotorhousing 14 by the ice. Thus, the pump portion P is readily activated.

The above embodiment may be modified as described below. The embodimentand the following modified examples may be combined as long as thecombined modified examples remain technically consistent with eachother.

In the embodiment, in the cold activation mode process, the inverter 60may execute only one of increasing the value of the activation currentsupplied to the motor 22 relative to when the normal activation modeprocess is executed or setting the supply duration of the activationcurrent to the motor 22 to be longer than that of when the normalactivation mode process is executed. More specifically, in the coldactivation mode process, the inverter 60 may execute at least one ofincreasing the value of the activation current supplied to the motor 22relative to when the normal activation mode process is executed orsetting the supply duration of the activation current to the motor 22 tobe longer than that of when the normal activation mode process isexecuted.

In the embodiment, the inverter 60 may execute control such that thesupply duration of the activation current is set so as to extend inaccordance with increases in the number of times the cold activationmode process is executed. For example, as the outside air temperature T1detected by the temperature sensor 63 becomes lower than the settemperature T2, it is likely that the driving rotor 20 and the drivenrotor 21 are more strongly adhered to the rotor housing 14. In such acase, the pump portion P may not be activated by the cold activationmode process executed only one time by the inverter 60. In this regard,the inverter 60 may set the supply duration of the activation current soas to extend in accordance with increases in the number of times thecold activation mode process is executed. In this configuration, thepump portion P may be activated with a fewer number of times ofexecution of the cold activation mode process, for example, as comparedto a configuration in which the inverter 60 invariably sets the supplyduration of activation current to be fixed regardless of increases inthe number of times of execution of the cold activation mode process.This reduces unnecessary power consumption while shortening the time foractivating the pump portion P.

In addition, when the supply duration of the activation current is setto one second, two seconds, and three seconds respectively for the firstto third times of the cold activation mode process and the pump portionP is activated by the third time of the cold activation mode process,the activation time is shorter than, for example, when the supplyduration of the activation current is invariably set to three secondsand the pump portion P is activated by the third time of the coldactivation mode process.

In the embodiment, the inverter 60 may execute control such that thesupply duration of the activation current is set so as to shorten inaccordance with increases in the number of times the cold activationmode process is executed, and such that the set supply duration of theactivation current is longer than the supply duration of the activationcurrent when the normal activation mode process is executed. Forexample, when the outside air temperature T1 detected by the temperaturesensor 63 is less than or equal to the set temperature T2, as theoutside air temperature T1 detected by the temperature sensor 63 becomescloser to the set temperature T2, it is highly likely that the drivingrotor 20 and the driven rotor 21 are not so strongly adhered to therotor housing 14 by ice. In such a case, when the inverter 60 executesthe cold activation mode process a few times, it is highly likely thatthe pump portion P immediately starts to be activated. In this regard,the inverter 60 may set the supply duration of the activation current soas to shorten in accordance with increases in the number of times thecold activation mode process is executed. This configuration minimizesthe time for which the inverter 60 supplies unnecessary activationcurrent to the motor 22 after the driving rotor 20 and the driven rotor21 are separated from the ice present between the inner wall of therotor housing 14 and the driving rotor 20 and the driven rotor 21, forexample, as compared to a configuration in which the inverter 60invariably supplies the activation current for a fixed durationregardless of increases in the number of times the cold activation modeprocess is executed. This reduces unnecessary power consumption.

In addition, when the supply duration of the activation current is setto one second, two seconds, and three seconds respectively for the firstto third times of the activation control and the pump portion P isactivated by the third time of the activation control, the activationtime is shorter than, for example, when the supply duration of theactivation current is invariably set to three seconds and the pumpportion P is activated by the third time of the activation control.

In the embodiment, the period of the activation current may be set so asto gradually extend during the cold activation mode process. Forexample, when the outside air temperature T1 detected by the temperaturesensor 63 is less than or equal to the set temperature T2, as theoutside air temperature T1 detected by the temperature sensor 63 becomescloser to the set temperature T2, it is highly likely that the drivingrotor 20 and the driven rotor 21 are not so strongly adhered to therotor housing 14 by ice. In such a case, even when the motor 22 quicklystarts to rotate at a high speed, the driving rotor 20 and the drivenrotor 21 are adequately separated from the ice present between the innerwall of the rotor housing 14 and the driving rotor 20 and the drivenrotor 21. In this regard, the inverter 60 gradually extends the periodof the activation current during the cold activation mode process. Inthis configuration, the motor 22 quickly starts to rotate at a highspeed as compared to in a configuration in which the period of theactivation current is invariably fixed. Thus, when the driving rotor 20and the driven rotor 21 are adhered to the rotor housing 14 by ice withrelatively low strength, the driving rotor 20 and the driven rotor 21are readily separated from ice present between the inner wall of therotor housing 14 and the driving rotor 20 and the driven rotor 21.Although the inverter 60 supplies the activation current to the motor 22even after the separation of the driving rotor 20 and the driven rotor21 from the ice present between the inner wall of the rotor housing 14and the driving rotor 20 and the driven rotor 21, unnecessary powerconsumption is reduced since the inverter 60 gradually extends theperiod of the activation current during the cold activation modeprocess.

In the embodiment, the values of the activation current, the lengths ofthe supply duration of the activation current, and the lengths of theperiod of the activation current during the cold activation mode processmay be combined with one another. More specifically, any setting may beused as long as the time for activating the pump portion P is shortenedor unnecessary power consumption is reduced as compared to when thevalue and the supply duration of the activation current are invariablyset to be fixed.

In the embodiment, the fuel cell pump is used as a pump that supplieshydrogen to a fuel cell that generates power by producing a chemicalreaction of hydrogen as a fuel gas with oxygen as an oxidant gascontained in the air. Instead, the fuel cell pump may be a pump thatsupplies air to the fuel cell.

In the embodiment, the fuel cell pump 10 is a Roots pump in which thepump portion P includes the driving rotor 20 and the driven rotor 21.Instead, the pump portion P may be, for example, a cascade pump or acentrifugal pump using impellers. More specifically, the fuel cell pump10 may have any configuration in which the pump portion P supplies thefuel cell 50 with hydrogen as fuel gas, air as an oxidant gas, or thelike.

In the embodiment, the temperature sensor 63 detects the outside airtemperature T1. Instead, for example, the temperature sensor 63 maydetect the temperature of the rotor chamber 25 to estimate the outsideair temperature T1. More specifically, any configuration for estimatingthe temperature environment of the outside of the fuel cell pump 10 maybe used.

In the embodiment, the pressure sensor 64 determines whether the pumpportion P is activated. Instead, the configuration may include a torquesensor that detects the torque of the motor 22 or the like. Morespecifically, the configuration may include any detector that detects achange between before and after activation of the pump portion P.

In the embodiment, the pressure sensor 64 determines whether the pumpportion P is activated. However, steps S14 and S18 executed by thepressure sensor 64 may be omitted. That is, in step S13 shown in FIG. 4, if the process fails to proceed from step S13 to step S15, step S13may be retried. Also, in step S17 shown in FIG. 4 , if the process failsto proceed from step S17 to step S15, step S17 may be retried.

In the embodiment, the driving rotor 20 and the driven rotor 21 may beshaped, for example, as three lobes or four lobes in a cross-sectionalview that is orthogonal to the rotational axial directions of thedriving shaft 16 and the driven shaft 17.

In the embodiment, the driving rotor 20 and the driven rotor 21 may be,for example, helical.

The inverter 60 may be configured to be circuitry including one or moreprocessors that execute various processes in accordance with a computerprogram (software). The inverter 60 may be configured to be circuitryincluding one or more dedicated hardware circuits such as an applicationspecific integrated circuit (ASIC) that execute at least some of thevarious processes or circuitry including a combination of the one ormore processors and the one or more dedicated hardware circuits, whichare described above. The processors include a CPU and memory such as RAMand ROM. The memory, that is, a non-transitory computer readable storagemedium, stores program codes or instructions configured to cause the CPUto execute processes. The memory includes any type of medium that isaccessible by a general-purpose computer or a dedicated computer.

Various changes in form and details may be made to the examples abovewithout departing from the spirit and scope of the claims and theirequivalents. The examples are for the sake of description only, and notfor purposes of limitation. Descriptions of features in each example areto be considered as being applicable to similar features or aspects inother examples. Suitable results may be achieved if sequences areperformed in a different order, and/or if components in a describedsystem, architecture, device, or circuit are combined differently,and/or replaced or supplemented by other components or theirequivalents. The scope of the disclosure is not defined by the detaileddescription, but by the claims and their equivalents. All variationswithin the scope of the claims and their equivalents are included in thedisclosure.

What is claimed is:
 1. A pump for a fuel cell, the pump comprising: apump portion configured to supply a fuel gas or an oxidant gas to thefuel cell; a motor configured to drive the pump portion; a controllerconfigured to control driving of the motor; a housing including a pumpchamber accommodating the pump portion, a motor chamber accommodatingthe motor, and a control chamber accommodating the controller; and atemperature detector configured to detect an outside air temperature,wherein the controller is configured to execute an activation controlthat is executed until the pump portion is activated, and a sensorlessvector control that is executed after the pump portion is activated, inthe activation control, the controller is configured to execute a normalactivation mode process when the outside air temperature detected by thetemperature detector is greater than a predetermined set temperature,and execute a cold activation mode process when the outside airtemperature detected by the temperature detector is less than or equalto the set temperature, in the cold activation mode process, thecontroller is configured to execute at least one of increasing a valueof an activation current supplied to the motor relative to when thenormal activation mode process is executed or setting a supply durationof the activation current to the motor to be longer than that of whenthe normal activation mode process is executed, and the controller isconfigured to shift from the activation control to the sensorless vectorcontrol after the pump portion is activated.
 2. The pump according toclaim 1, wherein the cold activation mode process includes increasingthe value of the activation current supplied to the motor relative towhen the normal activation mode process is executed, and setting thesupply duration of the activation current to the motor to be longer thanthat of when the normal activation mode process is executed, and amaximum of the value of the activation current in the cold activationmode process is greater than a maximum of the value of the activationcurrent in the normal activation mode process.
 3. The pump according toclaim 1, wherein the cold activation mode process is executed multipletimes.
 4. The pump according to claim 3, wherein the controller isconfigured to set the supply duration of the activation current so as toextend in accordance with increases in the number of times that the coldactivation mode process is executed.
 5. The pump according to claim 3,wherein the controller is configured to set the supply duration of theactivation current so as to shorten in accordance with increases in thenumber of times the cold activation mode process is executed, and theset supply duration of the activation current is longer than a supplyduration of the activation current when the normal activation modeprocess is executed.
 6. The pump according to claim 1, wherein thecontroller is configured to gradually shorten a period of the activationcurrent during the cold activation mode process.
 7. The pump accordingto claim 1, wherein the controller is configured to gradually extend aperiod of the activation current during the cold activation modeprocess.
 8. A method for controlling a pump for a fuel cell, wherein thepump includes a pump portion configured to supply a fuel gas or anoxidant gas to the fuel cell, a motor configured to drive the pumpportion, and a controller configured to control driving of the motor,the method comprising: an activation control that is executed until thepump portion is activated; and a sensorless vector control that isshifted from the activation control and executed after the pump portionis activated, wherein the activation control includes comparing apredetermined set temperature with an outside air temperature detectedby a temperature detector, which detects the outside air temperature,based on a result of the comparison, executing a normal activation modeprocess when the outside air temperature detected by the temperaturedetector is greater than the predetermined set temperature, andexecuting a cold activation mode process when the outside airtemperature detected by the temperature detector is less than or equalto the set temperature, and the cold activation mode process includesexecuting at least one of increasing a value of an activation currentsupplied to the motor relative to when the normal activation modeprocess is executed or setting a supply duration of the activationcurrent to the motor to be longer than that of when the normalactivation mode process is executed.
 9. The method according to claim 8,wherein the cold activation mode process includes increasing the valueof the activation current supplied to the motor relative to when thenormal activation mode process is executed, and setting the supplyduration of the activation current to the motor to be longer than thatof when the normal activation mode process is executed, a maximum of thevalue of the activation current in the cold activation mode process isgreater than a maximum of the value of the activation current in thenormal activation mode process, and the cold activation mode process isexecuted multiple times.